11/14/2014
Consider the atomic radii of fluorine (F) and nitrogen (N). Which statement is true?
Which of these atoms or ions do you expect to have the largest radius?
a) Fluorine has a smaller radius because it is closer to a stable closed‐shell configuration
b) Fluorine has a larger radius because it has more electrons
c) Fluorine has a smaller radius because its electrons experience a greater effective nuclear charge
d) Fluorine has a larger radius because its electrons experience greater e–‐e– repulsion
1
General trend: r ↓ up and to the right
Periodic property trends reflect orbital energies, which are best explained in terms of
QN n (up/down column) and Zeff (across row)
a) F–
b) Cl–
c) S2–
d) As3–
e) Sr2+
As3– and Sr2+ both have 36 electrons, with the 4s23d104p6 valence electron configuration of [Kr]. However, As3– has a lower Zeff (and so higher (–) charge) than Sr2+ and so has the larger radius.
2
Which atom has the lowest ionization energy?
Ionization energy measures ΔH for A ⎯→ A+ + e–
a) Ge
b) Ga
c) S
d) Cl
e) F
3
The IE of Na (5.14 eV) is lower than that of Mg (7.65 eV). Why? a) When Na loses an electron, it forms stable Na+. b) Na loses a single electron to form a closed shell, which is favourable. Mg loses an electron from a closed subshell, which is not.
c) The e–‐e– repulsion in the Mg 3s2 configuration releases more energy when an electron is lost.
d) Mg has a higher Zeff than Na, so its 3s electrons require more energy to remove.
e) Mg has a smaller atomic radius.
7.9 eV
6.0 eV
10.4 eV
13.0 eV
17.4 eV
General trend: IE ↑ up and to the right
• Ga and Ge will lose an n = 4 e–, so higher energy e–
(easier to remove) than S, Cl, F
• Ga has a lower Zeff than Ge, so electrons held less tightly, and higher energy e– (easier to remove)
133 pm
181 pm
184 pm
202 pm
118 pm
0
4
Periodic properties reflect orbital energies, which are best explained in terms of QN n (up/down a column) and Zeff (across a row).
E
IE Na
IE Mg
Na
Mg
Zeff
1
11/14/2014
Why is the IE of Al (5.99 eV) lower than that of Mg (7.65 eV)? Which of the following atoms has a diamagnetic ground state electronic configuration?
a) as expected, IE ↓ left‐to‐right across the row
b) removing an electron from Al is favourable, because it restores a stable closed subshell
c) Al loses a higher‐energy 3p electron, while Mg loses a lower‐energy 3s electron
d) atomic radius decreases across the row, which increases electron repulsion and makes it easier to remove an electron
5
Mg: [Ne]3s2 Al: [Ne]3s23p1
E
Discontinuities in periodic properties are best explained in terms of changes in the electronic configurations and orbital energies.
a)
b)
c)
d)
e)
diamagnetic means zero unpaired electrons (upe) 0
IE Al
IE Mg
3p
3s
3s
Mg
B
O
Mg
Fe
more than one of these could be diamagnetic
Al
Zeff
6
B: Z = 5, [He]2s22p1
O: Z = 8, [He]2s22p4
Mg: Z = 12, [Ne]3s2
Fe: Z = 26, [Ar]4s23d6
[↑↓] [↑][ ][ ] 1 upe, paramagnetic
[↑↓] [↑↓][↑][↑] 2 upe, paramagnetic
[↑↓] 0 upe, diamagnetic
[↑↓] [↑↓][↑][↑][↑][↑] 4 upe, paramagnetic
2